Methods and systems for energy-efficient drying of co-products in biorefineries

ABSTRACT

A method is disclosed for improving the energy efficiency of biorefinery drying operations through integration of a dryer that utilizes the heat of condensation of process vapors to dry material whose emissions are captured with energy recovery. The dryer separates clean process vapors (e.g., ethanol) and steam from vapors containing volatile organic compounds and entrained materials, to minimize the need for vapor cleanup. An indirect dryer condenses vapors in a tube dryer similar to a steam tube dryer, but utilizing compressed process vapors, transferring the heat to wet material undergoing drying. The resulting exhaust vapors are either directed to a process stage that requires heat (e.g., distillation) and minimizes the need for vapor cleanup or to an out-of-contact heat exchanger that produces vapors for process use, or to another dryer as an additional effect. Mechanical-vapor recompression or thermal-vapor recompression are employed to produce vapors that optimize overall energy recovery.

PRIORITY DATA

This patent application is a non-provisional application claimingpriority to U.S. Provisional Patent App. No. 62/800,044, filed on Feb.1, 2019; and U.S. Provisional Patent App. No. 62/857,619, filed on Jun.5, 2019, each of which is hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention generally relates to drying, and methods andsystems for improving the energy efficiency of drying operations.

BACKGROUND OF THE INVENTION

Bio-fermentation products, which include biofuels, biochemicals, andco-products such as dried distillers grains, are the result of theinvestment of significant energy. A biological raw material is grown andthen converted by chemical processing to a purified liquid fuel, as wellas drying of co-products such as dried distillers grains. Each steprequires energy-intensive stages which include distillation of thebiofuel and co-product drying. Conventional, first-generation methodsemployed at bio-distillery plants expend significant energy indistillation and drying, with the total process energy being aboutone-third of the energy contained in the produced biofuel. Theinefficiencies of these methods negatively impact producer economics aswell as the environmental footprint ascribed to the process.

The process energy consumed in distilling and co-product dryingtypically constitutes the largest energy requirement in the productionlife cycle for ethanol or other fermentation products. The distillationenergy in a standard bio-fermentation distillery represents from 40% to60% of the total process energy. “Total process energy” refers to directheating of processes by burning fuels, plus the electrical energyrequired for mechanical power used in pumping, stirring, grinding, etc.

Distillation systems are designed to meet a quality requirementappropriate for product market quality while meeting regulatoryenvironmental emission standards. First-generation distillation systemsin biofuels processing were implemented when simplicity was highlyprized—thus the environmental concerns related to energy usage werelargely relegated to minimizing associated emissions. Production wasvalued over minimizing the total process energy consumed or the impactof process inefficiencies on the environment. Today, policies andregulatory initiatives targeting the reduction of greenhouse-gasemissions are impacting consumers and producers of energy, creatingincentives for improving energy efficiency and minimizing environmentalfootprints.

Examples of regulation impacting energy consumers and producers includeCalifornia's Low Carbon Fuel Standard (LCFS) and the U.S. EPA's CleanPower Plan. The LCFS models fuel pathways to assign a Carbon Intensity(CI) to fuels, reflecting a fuel's lifecycle carbon dioxide emissions. Afuel producer's pathway, reflecting the CI for their process, generatescredits or requires the purchase of credits from other producers to meetCalifornia's CI targets. These credits are traded on an exchange thatestablishes their value and permits monetization by producers.Improvements in process energy efficiency are directly rewarded throughthe LCFS system, incentivizing investments in energy efficiency.Energy-efficient systems are desired because the LCFS incentivesdirectly reward producers for reducing their energy requirements, evenwhen low energy prices provide little or no incentive to make suchinvestments.

In view of the foregoing challenges, what are needed are improvements inoverall energy efficiency and optimization for new or existingbiorefineries employing distillation and/or co-product drying.

SUMMARY OF THE INVENTION

Some variations of the invention provide a method of energy-efficientdrying of a wet material in a biorefinery, the method comprising:

(a) providing a wet material containing a liquid phase of a firstproduct, a solid phase of a co-product, and water;

(b) thermally treating the wet material to obtain a process vaporcontaining the first product and a process liquid containing theco-product;

(c) increasing the pressure of the process vapor;

(d) heating at least a portion of the process liquid in an indirectdryer by condensing the process vapor that is out of contact with theprocess liquid, whereby heat of condensation of the process vapor isutilized for drying the process liquid;

(e) recovering a dryer exhaust stream derived from drying the processliquid; and

(f) optionally, separating the dryer exhaust stream into an exhaustvapor stream and an exhaust solids stream.

In some embodiments, at least a portion of the dryer exhaust stream or,if step (f) is conducted, the exhaust vapor stream, is compressed andreturned to step (b) to provide heat for thermally treating the wetmaterial, thereby recovering heat contained in the dryer exhaust stream.In certain embodiments, step (c) together with the dryer exhaust streamor the exhaust vapor stream being compressed and returned to step (b),forms a recompression loop, and at least 50%, 60%, 70%, 80%, 90%, 95%,99%, or essentially all of the thermal energy demand of the biorefineryis provided by the recompression loop.

When step (f) is conducted, at least a portion of the exhaust vaporstream may be compressed and used to heat another stream within thebiorefinery, thereby recovering heat contained in the exhaust vaporstream. For example, a second process vapor may be generated fromanother stream, wherein the second process vapor is compressed and fedto a second indirect dryer, and wherein heat of condensation of thesecond process vapor is utilized for drying within the second indirectdryer acting as an additional effect. The second indirect dryer furtherdries the co-product. In this configuration, the (first) indirect dryerin step (d) is an effect within a multiple-effect heat-exchange system.

When step (f) is conducted, at least a portion of the exhaust vaporstream may be condensed in a process stream containing the samecomponents as the exhaust vapor stream, to reduce the amount of theexhaust vapor stream being emitted to the atmosphere. Alternatively, oradditionally, at least a portion of the exhaust vapor stream, or acompressed form thereof, may be condensed using an out-of-contact heatexchanger, to reduce the amount of the exhaust vapor stream beingemitted to the atmosphere.

In preferred embodiments, step (b) utilizes distillation. In preferredembodiments, step (c) utilizes mechanical vapor recompression, thermalvapor recompression, or a combination thereof.

In some embodiments, in step (d), the process liquid is also heated withprocess steam that is out of contact with the process liquid, whereinthe heat of steam condensation and the heat of condensation of theprocess vapor are co-utilized for drying the process liquid.

The method may further include recovering, from the indirect dryer, acondensed form of the process vapor in a product stream. The method mayfurther include recovering, from the indirect dryer, a dried form of theco-product. In certain embodiments, the biorefinery is an ethanol plant,the first product is ethanol, and the co-product is dried distillersgrains.

Other variations of the invention provide a method of energy-efficientdrying of a wet material in a biorefinery, the method comprising:

(a) providing a wet material containing a liquid phase of a firstproduct, a solid phase of a co-product, and water;

(b) thermally treating the wet material to obtain a process vaporcontaining the first product and a process liquid containing theco-product;

(c) heating at least a portion of the process liquid in an indirectdryer by condensing the process vapor that is out of contact with theprocess liquid, whereby heat of condensation of the process vapor isutilized for drying the process liquid;

(d) recovering a dryer exhaust stream derived from drying the processliquid; and

(e) separating the dryer exhaust stream into an exhaust vapor stream andan exhaust solids stream,

wherein at least a portion of the exhaust vapor stream is compressed andreturned to step (b) to provide heat for the thermally treating, therebyrecovering heat contained in the dryer exhaust stream.

In some embodiments of these methods, at least a portion of the exhaustvapor stream is compressed and used to heat another stream (besidesthermally treating the wet material) within the biorefinery, therebyrecovering additional heat contained in the exhaust vapor stream.

In some embodiments, the method further includes recovering, from theindirect dryer, (a) a condensed form of the process vapor in a productstream (e.g., ethanol) and (b) a dried form of the co-product (e.g.,dried distillers grains).

Some variations of the invention provide a system for energy-efficientdrying of a wet material in a biorefinery, the system comprising:

(i) a thermal-treatment unit configured for separating a wet materialinto a process vapor stream and a process liquid stream, wherein the wetmaterial contains a liquid phase of a first product, a solid phase of aco-product, and water, wherein the process vapor stream contains thefirst product, and wherein the process liquid stream contains theco-product;

(ii) a first compressor in flow communication with the process vaporstream of the thermal-treatment unit, wherein the first compressor isconfigured for increasing the pressure of the process vapor stream;

(iii) an indirect dryer in flow communication with the first compressor,wherein the indirect dryer is configured to heat the process liquidstream by condensing the process vapor stream, whereby heat ofcondensation of the process vapor stream is utilized for drying theprocess liquid stream, and wherein the indirect dryer is configured witha dryer exhaust stream as an output; and

(iv) optionally, a dryer-exhaust separation unit configured to separatethe dryer exhaust stream into an exhaust vapor stream and an exhaustsolids stream.

In some system embodiments, the thermal-treatment unit is one or moredistillation columns. In some embodiments, the first compressor is amechanical vapor recompression unit or a thermal vapor recompressionunit. The indirect dryer may be part of a multiple-effect heat-exchangesubsystem.

Some systems further comprise a second compressor in flow communicationwith the dryer exhaust stream or, if the dryer-exhaust separation unitis present, with the exhaust vapor stream. The second compressor may beconfigured for increasing the pressure of the exhaust vapor stream, theprocess vapor stream, or both the exhaust vapor stream and process vaporstream.

In some embodiments, the second compressor is a mechanical vaporrecompression unit or a thermal vapor recompression unit.

When the dryer-exhaust separation unit is present, the system maycomprise an out-of-contact heat exchanger in flow communication with theexhaust vapor stream, or a compressed form thereof. Alternatively, oradditionally, the system may comprise a second indirect dryer that isconfigured to further dry the co-product.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts an exemplary process flow for a biorefinery with productdistillation and co-product drying, wherein compressed distillationvapor is used, rather than steam, to dry the co-product, and wherein theexhaust from drying is compressed and returned to drive distillation,forming a compression loop that reduces overall energy usage.

FIG. 2 depicts an exemplary process flow for a biorefinery with productdistillation and co-product drying, wherein compressed distillationvapor is used, rather than steam, to dry the co-product, and wherein theexhaust from drying is passed to an out-of-contact heat exchanger orreboiler to recover the dryer heat as steam that is returned to drivedistillation, forming a compression loop that reduces overall energyusage.

FIG. 3 depicts an exemplary process flow for a biorefinery with productdistillation and co-product drying, wherein compressed distillationvapor is used, rather than steam, to dry the co-product, and wherein theexhaust from drying is passed to an out-of-contact heat exchanger orreboiler to drive an additional steam tube dryer in a cascadedconfiguration for additional drying capacity, forming a compression loopthat reduces overall energy usage.

These and other embodiments, features, and advantages of the presentinvention will become more apparent to those skilled in the art whentaken with reference to the following detailed description.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Certain embodiments of the present invention will now be furtherdescribed in more detail, in a manner that enables the claimed inventionso that a person of ordinary skill in this art can make and use thepresent invention. All references herein to the “invention” shall beconstrued to refer to non-limiting embodiments disclosed in this patentapplication.

Unless otherwise indicated, all numbers expressing conditions,concentrations, yields, and so forth used in the specification andclaims are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending at least uponthe specific analytical technique. Any numerical value inherentlycontains certain errors necessarily resulting from the standarddeviation found in its respective testing measurements.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly indicates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as is commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. If a definition set forth in this section is contrary to orotherwise inconsistent with a definition set forth in patents, publishedpatent applications, and other publications that are incorporated byreference, the definition set forth in this specification prevails overthe definition that is incorporated herein by reference.

The term “comprising,” which is synonymous with “including,”“containing,” or “characterized by” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps. “Comprising”is a term of art used in claim language which means that the named claimelements are essential, but other claim elements may be added and stillform a construct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step,or ingredient not specified in the claim. When the phrase “consists of”(or variations thereof) appears in a clause of the body of a claim,rather than immediately following the preamble, it limits only theelement set forth in that clause; other elements are not excluded fromthe claim as a whole. As used herein, the phrase “consisting essentiallyof” limits the scope of a claim to the specified elements or methodsteps, plus those that do not materially affect the basis and novelcharacteristic(s) of the claimed subject matter.

With respect to the terms “comprising,” “consisting of,” and “consistingessentially of,” where one of these three terms is used herein, thepresently disclosed and claimed subject matter may include the use ofeither of the other two terms. Thus in some embodiments not otherwiseexplicitly recited, any instance of “comprising” may be replaced by“consisting of” or, alternatively, by “consisting essentially of.”

The present invention is premised on energy integration for improvingthe energy efficiency of biorefineries or other process plants. In somevariations, a method is disclosed for improving the energy efficiency ofdrying operations through integration of a dryer that utilizes the heatof condensation of process vapors alone, or in combination with processsteam, to dry material whose emissions are captured and directed to aprocess where heat of condensation of the process vapors may beutilized.

Tube dryers are conventionally used in series to progressively drymaterials with the material discharged from earlier-stage dryers feedinglater stages where further drying is accomplished. In these designs,each dryer condenses steam with the condensate returned to a steamgenerator for reheating and conversion back into steam. The recovery andreuse of the steam raised from drying has not been used inbiorefineries, since the conventional methods of drying driven by heatedair cannot easily nor efficiently be used as cascaded heat indistillation. Variations of the present invention utilize recovery ofprocess vapor heat of condensation by employing process vapor ratherthan process steam to operate an indirect dryer, thereby improvingoverall process energy efficiency. An “indirect dryer” means that thematerial being dried is heated indirectly from a heating medium, ratherthan directly (physical mixing).

In particular, the indirect dryer employed herein condenses vapors usinga cooling medium (e.g., water contained in the wet material) on theoutside of tubes, but using process vapors rather than steam alone totransfer heat to the wet material undergoing drying. This heat vaporizesliquid in the wet material. The resulting vapors, which containvolatilized liquid product and potentially volatilized organiccompounds, volatilized inorganic compounds, and suspended or entrainedsolids, are directed to (a) a process stage that requires heat andminimizes the need for vapor cleanup or to (b) an out-of-contact heatexchanger that produces vapors for process use or to (c) another dryer,acting as an additional effect, or a combination thereof.

Indirect dryers disclosed herein may also form multiple effects thatcascade heat from dryers condensing higher pressures and temperatures todryers condensing lower pressures and temperatures of steam and/orprocess vapors. The indirect dryer may separate clean process vapors andsteam from vapors containing volatile organic compounds and entrainedmaterials, and return heat in a manner that minimizes the need for vaporcleanup and system cleaning requirements.

In some embodiments, an indirect dryer employs a rotary steam-tube dryerdesign, except that a process vapor (comprising something other thanwater) rather than steam is condensed. The drying is accomplished by theheat of vaporization. In some embodiments, tube dryers are employed witha bundle of tubes inside the dryer, and the dryer body has little or noair for assisting in the drying. A tube dryer generally operates at alower temperature than other dryers and rotates at a slower speed.Material tumbles gently around the tubes that rotate with the shell.

The concept of mechanical vapor compression in distillation has beendeployed in reducing process requirements in refining for many decades.It has also been widely deployed in water desalination and processevaporation. Mechanical vapor compression, when used in distillation,recycles the heat of distillation by a closed heat pump, as disclosed,for example, in U.S. Pat. Nos. 4,340,446, 4,422,903, 4,539,076,4,645,569, 4,692,218, 4,746,610, 5,294,304, 7,257,945, 8,101,217,8,101,808, 8,114,255, 8,128,787, 8,283,505, 8,304,588, 8,535,413, and8,614,077, which are hereby incorporated by reference herein. Thermalvapor compression, when used in distillation, evaporation, dehydration,and drying, recycles latent heat by a closed heat pump, as disclosed forexample in U.S. Pat. Nos. 5,772,850, 4,536,258, and 4,585,523, which arehereby incorporated by reference herein. These methods of energyrecovery have been rarely utilized, however, in the distillationprocesses of bio-fermentation producers.

In this disclosure, mechanical vapor recompression (MVR) and/or thermalvapor recompression (TVR) are preferably used to produce vapor thatmeets conditions to best integrate and optimize energy recovery betweenprocesses, and to reduce overall process thermal energy usage in thebiorefinery. The heat of condensation of the compressed vapors providesenergy to the receiving process stage, such as drying. Heat exchangersutilizing multiple effects, thermal vapor recompression, and/ormechanical vapor recompression are used to balance process conditions byincreasing or decreasing vapor energy to serve process designrequirements. The number of dryer effects and the integration of MVR/TVRwill depend upon cost and design requirements for the integrated systemof interest.

All instances of “vapor compression,” “vapor recompression,” MVR, TVR,MVR/TVR, and the like mean mechanical vapor recompression, thermal vaporrecompression, or a combination thereof. Thermal vapor recompression mayalso be referred to as thermocompression or steam compression.

A wide variety of industries process materials that require drying.Current dryer designs transfer heat through convection by contact with agas that has been heated to a temperature higher than that of thematerial to be dried, through conduction by contact with a solidmaterial hotter than the material to be dried, or through radiant heattransfer which heats material by transferring energy via electromagneticwaves, such as infrared, microwave, etc. A common characteristic of eachof these methods is that they transfer energy to the material fromprocess steam created in a boiler or electricity, which is also usuallycreated from driving an electrical generator with steam that was createdin a boiler.

Many processing facilities include condensers that are used to coolvapors sufficiently to condense them into a liquid. The cooling water insuch condensers circulates between the condenser and cooling towers oran air-cooled heat exchanger. Because the vapors do not contain enoughenergy to be effectively reused in the facility's process, the heat ofcondensation is conventionally lost. By upgrading these process vaporsthrough mechanical vapor recompression or thermal vapor recompression,if needed, or directly transferring the vapors without pressure increaseto a dryer where the process vapors can be condensed, the heat ofcondensation that would otherwise be lost in the condenser can beutilized. Another method for recapturing the heat of condensationemploys a plurality of dryers as multiple effects (or a single dryerconfigured with multiple-stage effects) in which the heat otherwise lostin dryer exhaust is directed to another dryer, either directly orthrough vapor generation via a heat exchanger.

As an example of the general principles taught herein, a distillationprocess may be combined effectively with a drying process. The followingdescription is directed to typical ethanol plant distillation,dehydration, evaporation, and distillers-grains drying as a non-limitingexample of the disclosed method and system. All instances of“distillery” in this specification may be replaced with “biorefinery”and vice-versa.

It will be understood by a skilled artisan that the present invention isby no means limited to the biorefinery being an ethanol plant. Theprinciples disclosed herein may be applied to a wide variety ofindustrial processes such as wood pulp processing, food processing,brewing, and mineral processing, for example.

In addition, as will be appreciated by a person of ordinary skill in theart, the principles of this disclosure may be applied to manybiorefinery configurations beyond those explicitly disclosed ordescribed in the drawings hereto. Various combinations are possible andselected embodiments from some variations may be utilized or adapted toarrive at additional variations that do not necessarily include allfeatures disclosed herein. In particular, while some embodiments aredirected to ethanol as the primary biofuel/biochemical, the presentinvention is by no means limited to ethanol. For example, the inventionmay be applied to ABE fermentation producing a mixture of acetone,n-butanol, and ethanol. One or more additional distillation or otherseparation units may be included to separate components of afermentation mixture. Also, in some embodiments, the primary product isless volatile than water (at atmospheric pressure), rather than morevolatile, as is the case with ethanol. An example of abiofuel/biochemical less volatile than water is isobutanol.

Most distillation processes heat beer fed to a distillation column withsteam to raise its temperature to the beer's boiling point and thencontinue to add energy with steam as needed to overcome the beer's heatof evaporation or latent heat, converting the ethanol in the beer intovapors. Ethanol's lower boiling point (versus water) causes the ethanolto vaporize and exit the top of the distillation column. The solids inthe beer, along with water and other liquids with boiling points higherthan that of ethanol, are collected in the bottom of the distillationcolumn and then transferred to a centrifuge where a wet cake containingsolids and a significant proportion of liquids is separated from aliquid centrate. This wet cake is typically transferred to a dryer wherethe solids are dried to a moisture level appropriate for storage andshipping. Meanwhile, the alcohol vapors exiting the top of thedistillation column are typically directed to a water-cooled condenserwhere they condense, transferring their heat of condensation tocondenser cooling water prior to transfer of the condensate to adehydration process for final upgrading to a marketable ethanol product(as required by azeotropic limitations in making high-purity ethanol).

In variations of the present invention, the ethanol process vapor isredirected compared to conventional operations. Rather than being sentto a condenser, the process vapor is sent to a dryer, such as a steamtube dryer. A steam tube dryer is conventionally heated solely byprocess steam, but in the process herein the tube dryer (or otherindirect dryer) is heated by process vapor. The ethanol vapors arecondensed within the indirect dryer and the process-vapor heat ofcondensation is transferred to the wet cake, rather than being lost tocondenser cooling water. The condensed alcohol vapors may then betransferred as a liquid to the dehydration process as they would havebeen if they had been condensed in a condenser. The vaporized liquidremoved from the wet cake is transferred to the distillation columnwhere the heat of condensation (of the vaporized liquid) is recovereddirectly or through condensation in a heat exchanger and used tovaporize ethanol in the beer feed. Alternatively, or additionally, thevaporized liquid may be transferred to another dryer and condensed,recapturing the heat of condensation for use in further drying.

An important benefit in some embodiments is the separation betweenrelatively clean and relatively dirty vapors. The vapors exiting the topof the distillation column are relatively clean and may be condensed inthe tubes of a dryer with minimal concern for deposits building up inthe tubes, requiring periodic cleaning. The vapors exiting the dryer arerelatively dirty, but they may used to heat beer which is much dirtier,where “dirty” means the presence of contaminants that might formdeposits or contaminate process flows and necessitate periodic cleaningor treatment. The dryer exhaust may also be directed to anout-of-contact heat exchanger or reboiler where the dirty exhaustcondenses on one side of the heat exchanger, passing the heat to a cleanmedium that may be used to supplement steam generation or drive acascaded tube dryer. Conventionally, emissions from dryers requiretreatment through subjection to high temperatures for the time requiredto oxidize volatile organic compounds in a thermal oxidizer. Bycondensing these emissions in a distillation column, the quantity ofvapors requiring treatment through thermal oxidation is minimized, ifnot eliminated. Considerable value may be realized through recovery ofpreviously lost energy and elimination of both equipment and inefficienttreatment of dryer emissions.

In other applications, the method and system may be applied byidentifying points in a facility's process where significant latent heatis lost through condensers and bypassing those condensers to recover thelatent heat by condensing vapors in a dryer. Also, system designs may beoptimized through identification of clean and dirty process vaporstreams that may be condensed in a process block that minimizestreatment requirements and integrates with dirty dryer emissions andclean dryer heating vapors.

In one aspect, a method and system for drying materials is provided, inwhich a condensing dryer is integrated with other plant processes torecover the heat of condensation of clean process vapors for use indrying, and contaminated dryer exhaust is returned to processes directlyor indirectly via an out-of-contact heat exchanger for recovery of thedryer exhaust's heat of condensation.

In another aspect, mechanical vapor recompression and/or thermal vaporrecompression assists in recovering the heat of condensation from vaporsproduced in distillation and drying, providing a reduction in processthermal energy by the addition of mechanical energy for driving themechanical recompression.

In another aspect, mechanical vapor recompression and/or thermal vaporrecompression is sized or operated to match the thermal energy requiredin distillation with the thermal demand operated within the drying, andvice-versa, resulting in a reduced energy demand as a result of thereduction in standard steam energy demand due to energy recovered bymechanical vapor recompression and/or thermal vapor recompression in thedistillation and drying.

In another aspect, the dryer is sized or operated to match steam demandin the distillation process with the mechanical vapor recompressionand/or thermal vapor recompression adjusting the total thermal energydemand of the biorefinery in order that some or all of the thermalenergy is provided by the recompression loop between the dryer and thedistillation processes.

In another aspect, the portion of the dryer exhaust consisting of steamwith volatile organics requiring treatment is minimized by condensingthe vapors in a process stream of similar composition and minimizing theamount of dryer exhaust gas produced by evaporation of liquids from thematerial being dried.

In another aspect, the portion of the dryer exhaust consisting of steamwith volatile organics requiring treatment is minimized by condensingthe vapors in an out-of-contact heat exchanger and minimizing the amountof dryer exhaust gas produced by evaporation of liquids from thematerial being dried.

In another aspect, the portion of the dryer exhaust consistingessentially of steam condenses in an out-of-contact heat exchanger andthe dryer exhaust gas produced by evaporation of liquids from thematerial being dried is compressed to drive an additional tube dryerthat increases the amount of water removed from the stillage coproductsof the fermentation.

In another aspect, mechanical vapor recompression and/or thermal vaporrecompression is added to a biorefinery where the heat of vaporizationin the distillation top product is passed to a dryer with vaporrecompression used, if necessary, to raise steam pressures and/ortemperatures to drive the distillation process, thereby completing thevapor recompression loop for the distillation.

In another aspect, mechanical vapor recompression is applied to adistillation top product that is used for drying and mechanical vaporrecompression is applied to dryer vapor exhaust to compress it andreturn it to distillation.

In another aspect, mechanical vapor recompression is applied to adistillation top product that is used for drying and thermal vaporrecompression is applied to dryer vapor exhaust to compress it andreturn it to distillation.

In another aspect, thermal vapor recompression is applied to adistillation top product that is used for drying and mechanical vaporrecompression is applied to dryer vapor exhaust to compress it andreturn it to distillation.

In another aspect, thermal vapor recompression is applied to adistillation top product that is used for drying and thermal vaporrecompression is applied to dryer vapor exhaust to compress it andreturn it to distillation.

The schematic drawings, FIG. 1, FIG. 2, and FIG. 3, depict examples ofprocess flows for a biofuels plant with distillation and dryingprocesses that are energy-integrated. These diagrams show a distillationprocess used for purification of a biofuel, such as ethanol, and thedrying of fermentation co-products, such as dried distillers grains.

As described in more detail below including with reference to drawingelements, the process of FIG. 1 includes distillation of beer feed withdistillation vapors being compressed and transferred to anout-of-contact wet cake dryer. The bottom product of the distillation isfed to a centrifuge where the coarse solids are separated as a wet cakeand sent to the dryer, and the fine-soluble components are split into astillage product, part of which is sent to the dryer with the wet cake,while the balance of the stillage is returned and reused in the biofuelsplant. The dryer, while condensing the vapors from the distillation,generates steam-containing vapors as the stillage in the wet cake isevaporated. The steam-containing vapors are then compressed andtransferred to the beer column to drive the distillation process. Aportion of the steam-containing vapors from the dryer is passed to athermal oxidation system for the removal of volatile organic components.A recompression loop is formed between the vapors of the distillationcolumn sent to the dryer-condenser and the dryer vapor exhaust which iscompressed to conditions effective for reuse in the distillation stage.

The schematic drawing FIG. 2 depicts a process in which the exhaust fromthe dryer is compressed prior to passing the dryer's heat to anout-of-contact heat exchanger or reboiler where the dryer heat isrecovered as steam used to drive the distillation.

The schematic drawing FIG. 3 depicts a process in which the exhaust fromthe dryer is compressed prior to passing the dryer heat to anout-of-contact heat exchanger as a reboiler where the dryer heat isrecovered as steam and used to drive an additional steam tube dryer in acascaded configuration. The cascaded heat multiplies the heat reuse,thereby providing additional drying capacity. The cascaded dryer exhaustfrom the final dryer in the series is compressed for use in driving thedistillation process.

In some embodiments, the amounts of thermal energy required to sustainthe distillation and drying stages are nearly equal in magnitude;therefore, the raised steam by the dryer may be compressed and fully orpartially reused to support the distillation stage.

FIGS. 1-3 depict bio-fermentation distillery and drying process stageswhich generally include the following stages:

(1) a distillation stage, where the fermented products are processed andthe biochemical top products are separated from the fermentation waterand distillers grains co-products;

(2) a condensation stage where the vapors from distillation stage 1 arepassed on to a drying system where the heat of distillation is lost tocooling water or where the vapors are compressed to recover the heat ofdistillation for use in dryer stage 4;

(3) a stillage handling stage for the bottom product of distillationstage 1 in which a centrifuge dewaters the co-products and the recoveredwet co-products of the fermentation pass to dryer stage 4;

(4) a dryer stage for the biochemical dewatered co-products from thebottoms of distillation stage 1, in which the wet cake is driedsufficiently to achieve a long shelf life as a stable feed product andthe raised vapors in the exhaust of the dryer pass into a compressorwhere the exhaust steam goes to drive distillation stage 1 and a portionis discarded, if necessary, through thermal oxidation stage 5 in whichvolatile co-products are destroyed; and

(5) a thermal oxidation stage, where volatile biochemical components offermentation are destroyed prior to the gasses being emitted to theatmosphere.

The general distillery process includes stages which all require energyin the form of thermal energy and/or mechanical/electrical energy. Theschematic diagrams (FIGS. 1-3) highlight the post-fermentation stages ofdistillation and drying where the finished products are brought tomarketable quality. The thermal energy required in a plant without vaporrecompression in distillation and without vapor recompression in dryingcan be off-set and replaced by the energy required for driving the vaporrecompression as depicted in FIGS. 1-3.

The process energy distribution in the distillation and drying processesof the distillery, as defined in stage 1 above, is adjusted as neededthrough the use of vapor recompression (MVR and/or TVR) to supply thethermal energy required for drying stage 4. Vapor recompression (MVRand/or TVR), in turn, passes a sufficient portion of the raised steamfrom dryer exhaust from stage 4 back to distillation stage 1.Distillation and drying usually represent the largest energy-consumingstages in the distillery and therefore provide the largest potentialopportunity for reducing the total energy consumed in the plant.

The fermentation product entering the distillation contains the desiredbiochemical product as a watery solution with other co-products, passingvia line 100 into the distillation system 110, where the biochemicalfuel product of the fermentation is fractionated for separation of thebiochemical fuel from the watery co-products. The biochemical passes asa vapor out of the distillation stage via line 120 and the wateryco-products pass out of the distillation stage as a liquid via line 200.

The distillation system, 110, yields a top product which has abiochemical product composition that (in the case of ethanol as thebiochemical) approaches an azeotrope with water or which may be nearpurity with respect to the desired biochemical. The azeotrope or nearlypure biochemical product passes out of the distillation system as vaporsvia the vapor line 120 to a compressor 130 (which may be a compressorsystem with multiple compressors and/or ancillary equipment). Thecompressor 130 increases the pressure and condensing temperature of thevapors as required such that the heat of vaporization represents ahigher quality of heat as needed for a heat supply to the dryer system150. In the case that the distillation is operated at sufficiently highpressure to drive the dryer without the need for additional compression,for example, compressor 130 may be omitted.

Distillation vapors of sufficient pressure, optionally compressed bycompressor system 130, pass via line 140 on to the dryer system 150,wherein the vapors condense within the dryer 150, providing the heat fordrying. The condensed vapors within dryer 150 are liquefied and pass outof the dryer 150 via a line 160 where the liquid condensate is splitbetween distillation reflux via line 170 and the finished product 190-Pvia line 180 (the label “-P” denotes a product of the process).

The watery co-products of distillation are a bottom product leaving thedistillation system 110 via the liquid line 200 passing to a centrifugesystem 210 where the wet coarse solids pass via line 220 to line 260 andthe remaining watery portion with soluble co-products passes via line230 where the flow is split with a portion of the water containingdissolved co-product is recovered (or further processed) as product240-P and the balance of the liquid passes to line 250, which iscombined with line 220 into line 260 and on to the dryer 150.

The dryer 150 drives steam off wet cake, which steam passes out of dryer150 via line 300, with the partially dewatered fermentable co-products,after being sufficiently dried, passing out of dryer 150 via line 270.The steam with volatile organics raised from drying the wet distillersco-products passes out of dryer 150 via line 300. The vapors raised bythe dryer contain particulate solids and condensates which pass tocyclone 310 where the particulate material in the vapor stream isseparated out and passes via line 320 (evaporated thin stillage or“syrup”) to a conveyer system 280 together with the dried co-productfrom line 270 where they are combined as finished product 290-P.Optionally, some or all of stream 270 may be recovered as a driedco-product without necessarily combining with stream 320. Optionally,some or all of syrup stream 320 may be recovered as a product withoutnecessarily combining with stream 270. Various combinations of streams290-P, 270, 320, and 240-P may be utilized.

The extent of drying in the indirect dryer(s) may be varied as desired.Generally, the product stream 290-P may vary from about 35 wt % solidsto about 95 wt % solids. In various embodiments, the product stream290-P is about 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or 90 wt %solids. The intermediate stream 270 may also be about 40, 45, 50, 55,60, 65, 70, 75, 80, 85, or 90 wt % solids.

The cyclone system 310 removes heavy particulate materials, passing theclean steam vapors with volatile organics via line 330 to compressor340. The pressurized vapors from the compressor are raised to asufficient pressure and condensing temperature to drive the distillationsystem 110 via line 380 (1 and 2). The vapors collected by compressor340 pass out via line 350 where a portion is removed and transferred tothermal oxidizing system 360, if required, with the oxidized residualpassing to the atmosphere as stream 370-P.

In FIG. 1, the largest portion of vapors from compressor 340 passthrough line 380 (1 and 2) and drive the distillation system 110directly. This occurs when the latent heat of the dryer exhaust isreleased through condensing the vapors in the distillation column. InFIG. 2, the vapors pass from compressor 340 to line 380 which passes thevapors to an out-of-contact heat exchanger 400 that condenses the vaporsand transfers the latent heat recovered, vaporizing a process liquidpassed to the heat exchanger via line 410. The generated vapors arepassed via line 430 (1 and 2) to the distillation column 110 with excessprocess liquid blow down passed via line 420. In FIG. 3, the vapors passfrom out-of-contact heat exchanger 400 via line 430 to compressor 440,then to line 450 that passes high-pressure vapors to an additional tubedryer 460. The compressed vapors in tube dryer 460 capture the heat ofcondensation to drive the dryer with the condensate passing back to anout-of-contact heat exchanger 400 via line 410 (1 and 2). In theembodiment of FIG. 3, the partially dried distillers cake and syrup,290-P, from tube dryer 150, enter the additional tube dryer 460, wherethe dried distillers grains pass via line 470 to material handling 480resulting in product 490-P. The generated steam vapors in the exhaustfrom tube dryer 460 pass via line 500 to cyclone 510 with dryer dustpassing via line 520 to material handling 480 and the exhaust vaporspassing via line 530 to compressor 540. The compressed steam vapors fromcompressor 540 pass via line 550 (1 and 2) to distillation system 110.

The steam driving distillation system 110 is delivered directly via line380 (1 and 2) in FIG. 1 and indirectly via line 430 (1 and 2) from heatexchanger 400 in FIG. 2. In both FIG. 1 and FIG. 2, and indirectly vialine 550 (1 and 2) from additional tube dryer 460 exhaust, the vaporsare sourced from dryer system 150 and compressor 340 increases thepressure and condensing temperature as required to meet processconditions for use in distillation system 110. In FIG. 3, the vapors aresourced from the additional tube dryer 460, having compressed steamvapors from out-of-contact heat exchanger 400, which is driven fromcompressed steam vapors from the exhaust of tube dryer 150. The biofuelsvapors from distillation system 110 may have the pressure and condensingtemperature increased, if needed, by compressor 130 for use in dryer150. In FIG. 1 and FIG. 2 the two compressors, 130 and 340, form acomplete recompression loop wherein the latent heat of distillation isdriven through the dryer cycle and returned to the distillation. In FIG.3 the three compressors, 130, 340, and 540, form a completerecompression loop wherein the latent heat of distillation is driventhrough the dryer cycle and returned to the distillation.

In some embodiments, compressors 130 (FIGS. 1-3), 340 (FIGS. 1-3),and/or 540 (FIG. 3) are not present, such as when the distillation heatis directly cascaded, or when distillation pressure is sufficient suchthat further pressure increase of vapor is not necessary.

In the process depicted in FIGS. 1-3, there are various stream splits.One skilled in the arts of biorefinery design/operation or chemicalengineering will be able to determine the split fractions in order toachieve the desired process outcome, while maintaining mass balance. Theprocess may be simulated to determine split ratios that best achieve thedesired energy integration.

For example, liquid condensate in line 160 is split between line 170(distillation reflux) and line 180 (product). The ratio of line 170 flowrate to line 180 flow rate is the reflux ratio. In principle, the refluxratio may be 0 when no liquid condensate is returned to the column(e.g., under a dynamic situation such as during column maintenance); thereflux ratio may be infinite when all liquid condensate is returned tothe column (e.g., total reflux under a dynamic situation such as plantstart-up). At steady state, a typical range of reflux ratios by mass isabout 0.1 to 1, such as about 0.2 to 0.8, but this will vary dependingon the product, process configuration, and beer quality. For ethanol, atypical range of reflux ratios is about 0.3 to 0.7, such as about 0.50to 0.66. Higher-quality beer streams generally allow for lower refluxratios. For biofuels other than ethanol, depending on purityrequirements and other factors, very high reflux ratios may be useful,such as about 1, 2, 3, 4, 5, or even higher. Also, in certainembodiments, a relatively high reflux ratio may be employed in order tooperate distillation above the optimum for the purpose of cascading adesired amount of heat to the indirect dryer.

Another example of a flow split in FIGS. 1-3 is the split of line 230(water plus soluble co-products) splitting into line 250 (conveying toindirect dryer) and product 240-P. The split ratio by mass of line 250to 240-P may vary, such as from 0 to about 10, e.g. about 0.1, 0.2, 0.5,1, 2, 3, 4, or 5.

Another example of a flow split in FIGS. 1-3 is the split of line 350into line 380(1) (or line 380 in FIGS. 2 and 3) versus that line goingto the thermal oxidizing system 360. The split fraction may be 0, i.e.all material going back to distillation, directly or indirectly, and nomaterial going to the thermal oxidizing system 360. In otherembodiments, the split fraction by mass may be about 0.1, 0.2, 0.3, 0.4,or 0.5, for example, calculated as the mass flow to the thermaloxidizing system 360 divided by the mass flow of line 380(1) in FIG. 1or line 380 in FIG. 2 or 3.

In should be noted that regarding FIGS. 1 to 3, specific unit operationsmay be omitted in some embodiments and in these or other embodiments,other unit operations not explicitly shown may be included. Variousvalves, pumps, meters, sensors, sample ports, etc. are not shown inthese block-flow diagrams. Additionally, multiple pieces of equipment,either in series or in parallel, may be utilized for any unitoperations. Also, solid, liquid, and gas streams produced or existingwithin the process may be independently recycled, passed to subsequentsteps, or removed/purged from the process at any point.

In certain embodiments, a combined heat and power (CHP) sub-system isincluded in the overall system. An optional CHP sub-system has a CHPengine and is configured to provide mechanical, electrical, and/orthermal energy for driving vapor compression, wherein the CHP sub-systemand vapor compression may be integrated and configured so that residualwaste heat of the CHP engine offsets process thermal energy usage in thebiorefinery.

For example, an MVR unit may be configured with a standard steamgenerator to reduce thermal energy required in the distillation. Theoptional CHP engine may be sized in concert with (i) mechanical demandof the MVR unit and (ii) thermal energy demand of the biorefinery. Thewaste heat recovered by a CHP system optionally provides at least someof the thermal energy demand of the biorefinery, and may drive anoptional TVR unit.

As another example using CHP, a TVR unit may be configured with astandard steam generator to reduce thermal energy required indistillation. The optional CHP engine may be sized in concert with (i)thermal demand of the TVR unit and (ii) thermal energy demand of thebiorefinery. The waste heat recovered by a CHP system optionallyprovides at least some of the motive vapor to drive a TVR vapor jetand/or provide for the thermal energy demand of the biorefinery.

The present invention also provides a process comprising, or adaptedfor, any of the disclosed methods. The biofuel or biochemical may beselected from the group consisting of methanol, ethanol, 1-propanol,2-propanol, n-butanol, isobutanol, 2-butanol, tert-butanol, acetone, andcombinations thereof. The biofuel or biochemical may also be selectedfrom organic acids, such as lactic acid, higher alcohols (e.g., C₅₊alcohols), alkanes, etc. As used herein, “biofuel,” “biochemical,”biofuel/biochemical” and the like shall refer to one or morefermentation products of interest. Co-products include, but are notlimited to, dried distillers grains (DDG), dried distillers grains withsolubles (DDGS), still bottoms, sugars, lignin, and exported energy.

The present invention encompasses a product produced by a processcomprising a disclosed method and/or a product produced by a disclosedsystem.

In various embodiments, the biomass feedstock may be selected fromagricultural crops and/or agricultural residues. In some embodiments,agricultural crops are selected from starch-containing feedstocks, suchas corn, wheat, cassava, rice, potato, millet, sorghum, or combinationsthereof. In some embodiments, agricultural crops are selected fromsucrose-containing feedstocks, such as sugarcane, sugar beets, orcombinations thereof.

Lignocellulosic biomass may also be used as the biomass feedstock.Lignocellulosic biomass includes, for example, plant and plant-derivedmaterial, vegetation, agricultural waste, forestry waste, wood waste,paper waste, animal-derived waste, poultry-derived waste, and municipalsolid waste. In various embodiments of the invention, the biomassfeedstock may include one or more materials selected from: timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, knots, leaves, bark, sawdust, off-spec paper pulp, cellulose,corn, corn stover, wheat straw, rice straw, sugarcane bagasse,switchgrass, miscanthus, animal manure, municipal garbage, municipalsewage, commercial waste, grape pumice, almond shells, pecan shells,coconut shells, coffee grounds, grass pellets, hay pellets, woodpellets, cardboard, paper, carbohydrates, plastic, and cloth. Mixturesof starch-containing and/or sucrose-containing feedstocks withcellulosic feedstocks, for example, may be used.

The throughput, or process capacity, may vary widely from smalllaboratory-scale units to full commercial-scale biorefineries, includingany pilot, demonstration, or semi-commercial scale systems. In variousembodiments, the process capacity is at least about 1 kg/day, 10 kg/day,100 kg/day, 1 ton/day (all tons are metric tons), 10 tons/day, 100tons/day, 500 tons/day, 1000 tons/day, 2000 tons/day, 3000 tons/day,4000 tons/day, or higher.

The biorefinery may be a retrofit to an existing plant. In otherembodiments, the biorefinery is a greenfield plant.

All publications, patents, and patent applications cited in thisspecification are incorporated herein by reference in their entirety asif each publication, patent, or patent application was specifically andindividually put forth herein. This specification hereby incorporates byreference commonly owned U.S. Pat. No. 9,925,476, issued Mar. 27, 2018,and U.S. Pat. No. 9,925,477, issued Mar. 27, 2018, and U.S. Patent App.Pub. No. 2018/0028934 A1, published Feb. 1, 2018.

In this detailed description, reference has been made to multipleembodiments of the invention and non-limiting examples and drawingsrelating to how the invention can be understood and practiced. Otherembodiments that do not provide all of the features and advantages setforth herein may be utilized, without departing from the spirit andscope of the present invention. This invention incorporates routineexperimentation and optimization of the methods and systems describedherein. Such modifications and variations are considered to be withinthe scope of the invention defined by the claims.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the variations of theinvention. Additionally, certain of the steps may be performedconcurrently in a parallel process, when possible, as well as performedsequentially.

Therefore, to the extent that there are variations of the inventionwhich are within the spirit of the disclosure or equivalent to theinventions found in the appended claims, it is the intent that thispatent will cover those variations as well. The present invention shallonly be limited by what is claimed.

What is claimed is:
 1. A method of energy-efficient drying of a wetmaterial in a biorefinery, said method comprising: (a) providing a wetmaterial containing a liquid phase of a first product, a solid phase ofa co-product, and water; (b) thermally treating said wet material toobtain a process vapor containing said first product and a processliquid containing said co-product; (c) optionally, increasing thepressure of said process vapor; (d) heating at least a portion of saidprocess liquid in an indirect dryer by condensing said process vaporthat is out of contact with said process liquid, whereby heat ofcondensation of said process vapor is utilized for drying said processliquid, wherein said process vapor in this step (d) is obtained fromstep (b) and/or step (c), if conducted; (e) recovering a dryer exhauststream derived from drying said process liquid; and (f) separating saiddryer exhaust stream into an exhaust vapor stream and an exhaust solidsstream.
 2. The method of claim 1, wherein at least a portion of saidexhaust vapor stream is compressed and returned to step (b) to provideheat for said thermally treating, thereby recovering heat contained insaid dryer exhaust stream.
 3. The method of claim 2, wherein step (c) isconducted, wherein step (c) together with said dryer exhaust stream orsaid exhaust vapor stream being compressed and returned to step (b),forms a recompression loop, and wherein at least 50% of the thermalenergy demand of said biorefinery is provided by said recompressionloop.
 4. The method of claim 3, wherein at least 90% of said thermalenergy demand of said biorefinery is provided by said recompressionloop.
 5. The method of claim 3, wherein essentially all of said thermalenergy demand of said biorefinery is provided by said recompressionloop.
 6. The method of claim 1, wherein at least a portion of saidexhaust vapor stream is compressed and used to heat a separate streamwithin said biorefinery, thereby recovering heat contained in saidexhaust vapor stream.
 7. The method of claim 6, wherein a second processvapor is generated from said separate stream, wherein said secondprocess vapor is compressed and fed to a second indirect dryer, andwherein heat of condensation of said second process vapor is utilizedfor drying, whereby said second indirect dryer further dries saidco-product.
 8. The method of claim 1, wherein at least a portion of saidexhaust vapor stream is condensed in a process stream containing thesame components as said exhaust vapor stream, to reduce the amount ofsaid exhaust vapor stream being emitted to the atmosphere.
 9. The methodof claim 1, wherein at least a portion of said exhaust vapor stream, ora compressed form thereof, is condensed using an out-of-contact heatexchanger to reduce the amount of said exhaust vapor stream beingemitted to the atmosphere.
 10. The method of claim 1, wherein step (b)utilizes distillation.
 11. The method of claim 1, wherein step (c)utilizes mechanical vapor recompression.
 12. The method of claim 1,wherein step (c) utilizes thermal vapor recompression.
 13. The method ofclaim 1, wherein said indirect dryer forms an effect within amultiple-effect heat-exchange system.
 14. The method of claim 1, whereinin step (d), said process liquid is also heated with process steam thatis out of contact with said process liquid, and wherein heat of steamcondensation and said heat of condensation of said process vapor areco-utilized for drying said process liquid.
 15. The method of claim 1,said method further comprising recovering from said indirect dryer acondensed form of said process vapor in a product stream.
 16. The methodof claim 1, said method further comprising recovering from said indirectdryer a dried form of said co-product.
 17. The method of claim 1,wherein said biorefinery is an ethanol plant, wherein said first productis ethanol, and wherein said co-product is dried distillers grains. 18.A method of energy-efficient drying of a wet material in a biorefinery,said method comprising: (a) providing a wet material containing a liquidphase of a first product, a solid phase of a co-product, and water; (b)thermally treating said wet material to obtain a process vaporcontaining said first product and a process liquid containing saidco-product; (c) heating at least a portion of said process liquid in anindirect dryer by condensing said process vapor that is out of contactwith said process liquid, whereby heat of condensation of said processvapor is utilized for drying said process liquid; (d) recovering a dryerexhaust stream derived from drying said process liquid; and (e)separating said dryer exhaust stream into an exhaust vapor stream and anexhaust solids stream, wherein at least a portion of said exhaust vaporstream is compressed and returned to step (b) to provide heat for saidthermally treating said wet material, thereby recovering heat containedin said dryer exhaust stream.
 19. The method of claim 18, wherein atleast a portion of said exhaust vapor stream is compressed and used toheat another stream within said biorefinery, thereby recoveringadditional heat contained in said exhaust vapor stream.
 20. The methodof claim 18, said method further comprising recovering, from saidindirect dryer, (a) a condensed form of said process vapor in a productstream and (b) a dried form of said co-product.